Hemp (Cannabis sativa L.) is a polymorphic species that synthesizes an array of bioactive metabolites, with cannabinoids and terpenoids constituting the major chemical classes. Until recently, the lack of legislative framework led to limited research on hemp’s plant protection and nutrition. Biostimulants have recently attracted scientific attention as sustainable alternatives to plant protection products (PPPs). Herein, we investigated the effects of biostimulant harpin (αβ) proteins and the PPP polysaccharide laminarin on hemp (cv. Futura 75), employing GC/EI/MS and ¹H NMR metabolomics. Analyses demonstrated that treatments induced distinct shifts in the metabolism of the plants, thus, enabling the discovery of metabolite-biomarkers of physiological adaptation, defense mechanisms (α-linolenic acid), and bioactivity (cannabinoids). Harpin and laminarin altered the concentration of bioactive compounds such as cannabidiol, essential amino acids including L-phenylalanine and GABA, salicylate, and caffeate. Pathway analysis revealed treatment-specific modulation of key metabolic networks, with harpin triggering early, yet transient activation of phenylpropanoid- and amino acid-related pathways before broad repression, whereas laminarin maintained a more balanced regulation, sustaining defense-related biosynthesis while preserving core primary metabolism. Results advance the understanding of molecular mechanisms underlying biostimulants’ action in hemp and support their potential for improving plant health and attributes of cannabis-derived products, providing insights for its sustainable cultivation.

Olive tree (Olea europaea L.) cultivation is increasingly challenged by climate change and the necessity for more sustainable crop management strategies. In this context, plant biostimulants have emerged as inputs of high potential for improving crop performance and resilience. Nonetheless, knowledge of their underlying biochemical mechanisms remains largely fragmented. Here, an untargeted GC/EI/MS-based metabolomics approach was employed to investigate the early metabolic responses of young olive trees to foliar application of two commercial biostimulants: a seaweed (SE)- and a harpin (HRP)-based formulation. Leaf samples were collected seven days post-treatment and were subjected to photosynthetic-content and metabolomics analyses. The former revealed no statistically significant differences in chlorophyll and carotenoid contents among treatments, indicating that photosynthetic pigment homeostasis was maintained. In contrast, metabolomics analysis demonstrated extensive and coordinated metabolic reprogramming induced by both products. SE treatments resulted in a primarily promoted growth-oriented metabolic profile, characterized by enhanced carbon utilization, modulation of antioxidant metabolism, activation of plastidial isoprenoid biosynthesis, and remodeling of the shikimate–phenylpropanoid pathway. Conversely, HRP treatments elicited a distinct stress-priming signature involving the accumulation of α,α-trehalose, phytol, and α-ketoglutaric acid, together with membrane lipid remodeling associated with improved osmoprotection and stress acclimation. These findings provide novel insights into the mode(s) of action of olive biostimulants and highlight the importance of metabolomics for identifying biochemical markers associated with enhanced plant resilience and sustainable olive production.